Experimental Evaluation of the Rate of Rise Technique for Measuring Outgassing Rates in a Vacuum

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Virginia Polytechnic Institute

With an increase of interest in space flight and vacuum research, there has been a corresponding increase in the need for values of outgassing rates of many materials. In space flight the knowledge of the outgassing rates of components and materials used in construction of space vehicles allow the determination of pressures within sections of the vehicle, the contamination level of critical components, and the reliability of vehicle components. In the construction of an ultra high vacuum facility, the knowledge of the value of the outgassing rates of construction materials allows the chamber to be constructed of low outgassing materials, minimizing the amount of gas evolving from the chamber walls. With the initiation of a research program, the outgassing rates of the chamber, test objects, and instrumentation are needed to determine the level of vacuum obtainable during the investigation.

With the increased need for outgassing rates, more emphasis has been placed on the measurement of outgassing rates. The literature reports several techniques for the measurement of outgassing rates. Of these techniques, the rate of rise method is simple and convenient to apply, and hence of much interest. Because it is simple and easily applied, the rate of rise technique has been used by many experimenters to measure the outgassing rates of various materials. However, some experimenters have rejected its use as they felt that the dynamic nature of the technique introduced large errors into the outgassing measurements. There is presently in the literature no technical evaluation of the rate of rise method as to the suitability or unsuitability for measuring outgassing rates.